Probing the blackhole is equivalent to perturbing this thermal state and the imaginary part of the frequency of decay determines the thermalization time-scale. From bulk perspective a prediction of the thermalization time-scale was first obtained in [1]}. On the boundary the scalar probe is coupled to a operator \(\mathcal {O}\)  with dimension \(\Delta _{\mathcal {O}}\)  in 2D CFT. Completely bypassing the string theoretic approach as espoused in [2]}, it can be shown [3]} that the location of the poles of the fourier transformation of the high temperature conformal autocorrelator of \(\mathcal {O}\)  exactly matches with the frequencies of QNMs obtained from bulk side calculations.
\(\Gamma ^{(decay)}\propto \frac{e^{-\omega \beta /2}}{\beta ^{2\Delta _{\mathcal {O}}-1}} \bigg \vert \Gamma \left(\Delta _{\mathcal {O}}+i\frac{\omega \beta }{2\pi }\right)\bigg \vert ^{2}\) 
\(\omega _{n}=-i\frac{2\pi }{\beta }(n+\Delta _{\mathcal {O}})\) 
